Process of treating sewage sludge



.. Patented Oct. 14-, 1924.

UNITED STATES, PATENT OFFICE. T

ANGUS HACLACHLAN, F PERTH AMBOY, NEW JERSEY, ASSIGNOR TO KACLACH- LANREDUCTION PROCESS 00., OF NEW YORK, N, Y., A CORPORATION OF DELA-WAIBCE.

PROCESS OF TREATING SEWAGE SLUDQ-E.

lio Drawing.

To all whom it may concern:

Be it known that I, ANGUS Msonscmnn, a citizen of the United States,residing at Perth Amboy, New Jersey, have invented 15 certain new anduseful Improvements in Processes of Treating Sewage Sludge, of which thefollowing is a clear, full, and exact description.

My invention relates to the purification l0 and dehydration of sewage,and more particularl to the treatment of sewage sludge. By slud g whichhas been preliminarily treatedv to cause a more or less separation ofthe solid 16 or semi-solid materials from the purely liquid content, andin which the liquid content has been reduced somewhat. Various 'methodshave heretofore been proposed to cause such a separation, and'one of the20 methods at resent in use is that known as the activa sludge method ofsewage disposaL This, as is well known, consists in conducting thesewage from the mains into tanks WhlCh are provided with means for 2introducing air to the sewage to be treated,

the passa e of air through this sewage aiding in v e development ofmicroscopic aerobic organisms which in the course of their growthoxidize the soluble solids in the sewage which then separate asflocculent gelatinous materiaL The sewage thus treated is usually thenrun into a settling tank or successively into sett tanks, where it isallowed to remain a. s cient time for the solids to settle to thebottom, the more or less pure water being decanted or otherwise removedfromthe top.

As a result of this, or equivalent preliminary treatment of sewage, thewatercontent 40 is reduced to such an extent that, whereas theproportion of solid matter to water in sewage is about 1 to 4000, insludge the proportion of solid to liquid is only 1 to 200.

It is to the treatment of this sludge that this application isparticularly directed.

A mrious problem which presents itself, however, is the matter ofhandling large uantities of very. light sludge which is prouced by theprocess above outlined. This sludge is ordinarily entirely innocuous asremoved from the treatment plant, but it is highly putrescible, that isthe organisms contained therein rapidly die when not kept in contactwith amp e air and food Com quently; the problem of disposing of the e,I mean sewage from the mains -Application filed April 12, 1922. SerialFe. 551,939.

sludge without nuisance has been a serious problem and undoubtedly hasbeen one of the chief draw-backs to more general adoption of theactivated sludge process.

By virtue of its gelatinous and putrescible nature, this sludge will not'eld to any of the usual commercial meth of removin water, such asfilter-presses, centrifuges an the like. It is evident that some methodof conditioning or pro-treating this sludge in order to changethephysical and biological characteristics must be employed before therecan be great hope of economical dewatering.

The sludge which remains has been in the past treated in a number ofways to recover the fertilizing content and sometimes the grease andammonia products, but great difiiculty has heretofore been experiencedin causing a further separation of the solid materials from the sludge,which at this stage contains in excess of 95% of water. It is notfeasible to subject this activated'sludge to a prolonged settlingprocess, otherwise the growth of anaerobic organisms is piermitted andthese soon kill or greatly was. en the aerobic bacteria, resulting inputrefaction of the mass.

It has been proposed to raise the temperature of this sludge to 30 G. or40 (land to treat it with sulphuric acid to aid in coaguiating its moreor less flocculent particles, and afterwards screening, filtering and d'ng the resultant products On account, owever, of the enormousquantities of water still contained in the sludge this process isexpensive, and it has been found in practice that the cloths used infiltering are soon clogged. Furthermore, a sludge cake which has beenproduced by. treatment 95 with sulphuric acid has been found difiicultto dry since it has a tendency to retain its water content.

Furthermore, when the sludge" is treated with sul huric acid there is a1sadvantage,,100 due to t e corrosive effect on the pipes, ma-- chineryand other equipment used By the present invention, I so treat the"sludge after activation that not only is its bacteria rendered innocuousbut at the same 105 time its gelatinous nature is brokendown so that theresulting material will be more amenable to dewatering.

For this purpose I prefer to use a gas having both a and ionizingaction, 110

' stopp and I have found that sulphur dioxide is eminently suitable forthis purpose, which may be cheaply supplied, as required, by the burningof crude sulphur in a suitable ty'ge hof burner.

e advantage of using a gaseous re-agent for conditioning this sludge, isthe fact that its introduction into a tank containing the sludge to betreated causes more or less violent agitation of the tank contents withthe result that the entire mass is thoroughly impregnated with there-agent in a very short period of time, causing the bacteria to berendered innocuous, and a thorough diffusion of the electrolytic agentso that coagulation of the colloidal solids is practicallyinstantaneous.

In the practice of my invention, activated sludge is withdrawn from thetreatment plant proper and subjected to sedimentation for a relativelyshort period to remove any free water from the sludge, by decantation.The sludge thus obtained is then introduced into a treatment tank ofconvenient size and shape, preferably a vertical, cylindrical tank witha hopper bottom. This treatment tank may be so designed that thetreatment of sludge can be conducted on either a continuous or anintermittent basis. Since the sterilizing and electrolytic gas is quitesoluble in the water content of the sludge, the size and shape of thetreatment tank are not very important provided ordinary precautions aretaken to insure intimate contact between the gas and sludge. For thisreason I prefer to introduce the raw sludge flow at or near the top ofthe tank, withdrawing it at or near the bottom, and at the same timeintroducing the gas throu h perforated pipes or grids at or near theottom, allow mg it to pass up through thdflowing sludge incounter-current direction giving maximum contact. In some cases I mayprefer to place three such tanks in series to eliminate a possibility ofshort circuiting and this arrangement enables me to treat at a high rateof flow.

Almost immediately upon the sulphur dioxide coming into contact with thesludge material a breaking down of the gelatinous nature of the solidconstituents of the-sludge takes place. The treatment is continued untilthis breaking down is com lete, the time depending upon the amount 0 gasmixture admitted and the quantity of material to be treated, after whichthe gas may be ed and the tank contents allowed to settle. Preferably,however, the tank contents is passed on to a settling tank where aninstantaneous precipitation of the solids takes place, with thedecantation of clear water, giving'a reduction in the volume of sludgesolids by about The sludge solids thus withdrawn are substantiallysterile in nature, with no offensive odor and are furthermore so changedin physical character that they may be easily further dewatered byfilter-pressing, centrifuging, draining on sand beds, etc. In some casesI prefer to draw direct from the treatment tank to the next dewateringstage such as filter presses, in order to avoid the delay entailed byfinal sedimentation. This fiirther treatment may consist in draining,pressing, drying or any combination of these steps, to still furtherreducethe liquid content.

The effect of applying the gas mixture to the sludge appears to producetherein an electrostatic change which converts the gelatinous solidsinto a more or less granular or porous form and in this form theexcessive water content may be easily decanted or J syphoned ofi and theresidue more QCOIIOmI- cally, quickly and conveniently pressed or dried.

My invention also contemplates treatin the activated sludge or thesludge forme in .anyother manner with S0 and steamv preferably byaspirating the fumes of burning sulphur with live steam. This may bemost advantageously done in an apparatus of-the kind shown and describedin my Patent #1559986, dated November 16, 1920.

Whether, however, the sludge is treated with SO or the S0 and steam, thegeneral procedure is substantially the same, as alread outlined, andineither case there is no visible evidence of free acids being liberatedduring or after the gas treatment. The beneficial effects of mytreatment seem to be due to an electrolytic and germicidal action ofsulphur dioxide under conditions in which it is used, rather than to achemical reaction.

Sewage sludge, particularly activated sludge which has been treated bythe sterilizing and electrolytic gas process described above, isconsiderably changed in hysical character and in suitable shape forfinal dewatering. The free water may be readily drained therefrom bypassing the .treated sludge onto some draining apparatus such as a sandbed, fine screen, etc., or, if it is preferred, the treated sludge maybe introduced into the standard filter press, where it readily-builds upa firm solid cake and with minimum clogging of the press cloths. Havingreduced the water by either draining or pressing, the resultant slud ecake is in excellent condition for final rying in a suitable dryer sinceit is more or less porous in nature and gives up its moisture quickly onthe application of heat. The dried product is easily disintegrated intodesirable form for marketing as a fertilizer.

An additional advantage resulting from my treatment process isthe factthat considerable nitrogen compounds are saved, due to the fact thatsterilization of bacteria prevents decomposition and gaseous evoluvtreatin tion of nitrogen compounds, and also dueto the fact that calciumsalts contained in the sludge tend to dissolve and pass off in thefilter liquor, thereby resulting in enrichment of the nitrogen contentof the final sludge. This effect of my treatment is highly importantsince one of the purposes of an acti-,

vated sewa e treatment plant is to produce a marketabe fertilizer whichmay more or less pa for the cost of sewage treatment. Since t efertilizing value of the sludge is directly clgplendent upon itsnitrogen 00,11- tent, it be seen that any treatment which tends toincrease same will have a direct bearing on the value of the sludge. Inactual practice I have found that the fertilizer produced from activatedsludge which has been treated by my process contains as hi h as moreammonia than sludge pr need without any treatment and contains as highas 40% more ammonia than sludge which has been treated with acids suchas sul huric.

This app ication is a continuation in part of my application Serial#482,254, filed Jul 2, 1921, and allowed October 12, 1921.

' at I claim as new is 1. The method of treating activated sludge whichconsists in brin the sludge into intimate contact with sulp ur dioxidefor a sufiicient time to break down the gelatinous nature of. the solidconstituents of the sludge.

2. The method of treating activated sludge which consists in bringin thesludge into intimate contact with sulphur dioxide for a suflicient timeto retard or destroy the putrefactive tendenc of the sludge and to breakdown the ge atinous nature of the solid constituents thereof.

3. The method of treating sewage sludge which consists in bringin thesludge into contact with hot sulphur 'oxide and steam for a sufiicienttime to break down the gelatinous nature of the solid constituents ofthe sludge.

4. The method of treating sewage sludge which consists in bringingl theslud into contact with hot sulphur 'oxide an steam for a suficient timeto retard or destroy the utrefactive tendenc of the sludge and to hreakdown the ge atinous nature of -the solid constituents thereof.

v5. The method of dehydrating and purifying sewage sludge which consistsin pres liminarily separating the or nic matter from the water to form aslu e and then the sludge thus formed with sulphur oxide fora sufiicienttime to break down the elatinous nature of the solid constituents tereof.

6. The method of dehydrating and p11-" rifying sewage sludge whichconsists in prewith hot SO 'and "steam-for a treatin the sludge thusformed with sulphur dloxide for a sufiicient time to retarc.

or destroy the putrefac'tive tendency. of the sludge and to break downthe gelatinous nature of the solid constituents thereof. I

7. The method of .dehydrating activated sludge whichconsists in treatinthe same with sulphur dioxide for a su cient time to break down thegelatinous nature of the solid constituents thereof, settling theresulting product, and removing the separated 10. The method ofdehydrating activated sludge which consists in treatin the same withsulphur dioxide for a s cient time to break down the gelatinous natureof the solid constituents thereof, settling the resulting product,removing the separated water and p and drying the residue.

11. The method of treating sewage sludge, which consists in bringing thesludge into contact with hot SO and steam, for a sufficient time. tocause separation of the solid constituents of the sludge.

12. The method ,oftreating activated sludge which consists in bringingthe sludge into contact with hot S0 and steam, for a suflicient time tocause separation of the solid constituents of the sludge.

13. The method of dehydrating and purifying sewage which consists inpreliminarily separating the or ic matter from the water to form a slu eand then treating the sludge thus formed with hot S0 and steam for asufiicient time to cause so aration of the solid constituents of the slu14.- The method of dehydrating sewage sludge which consists in treatfthe same cient time to cause separation of the solid constituents of thesludge, settling the resultant product, and removing the separatedwater.

15. The method of dehydrating sewage sludge which'consistsin treatin thesame with hot S0 and steam for asu cient time to cause separation of thesolid constituents of the sludgle, settling the resultant roduct, remo te separated water, an drying the resi ue.

16. The method of dehydrating sewagesludge which consists in treatingthe same with hot S0 and steam for a sufiicient time to cause separationof the solid constituents of the sludge, settling the resultant product,removing the separated water, and pressing 5 the residue.

17. The method of dehydrating sewage sludge which consists in treetinthe same with hot S0 and steam for a su cient time to cause separationof the solid constituents v of the sludge, settling the resultantproduct, 10 removing the se arated water, pressing and drying the resiue.

Signed at New York city, New York, this 11th day of April, 1922.

ANGUS MACLACHLAN.

